Bo Hagerman

Adaptive antennas for GSM and TDMA systems

Adaptive antennas have generated great interest in previous years, and at present several manufacturers and operators are separately or jointly performing field tests to gain more detailed knowledge of the potential of the technology. This article summarizes many of the experiences that have been collected since 1996 during field trials carried out for both GSM and TDMA (IS-136) by Ericsson in cooperation with two major network operators, Mannesmann Mobilfunk and AT&T Wireless Services.

Downlink relative co-channel interference powers in cellular radio systems

One method to achieve high capacity in cellular radio systems involves interference cancellation techniques at the receivers. To design and evaluate the performance of such interference cancellation receivers, it is essential to use realistic models of the co-channel interference. In the paper we study the ordered statistic of the relative co-channel interference, i.e. the ratio between the power level of i:th strongest interferer and the total co-channel interference power. Results from Monte-Carlo simulations show that for base stations on a symmetric grid, hexagonal cells or half-square Manhattan like street cells, the probability density functions (pdf) of the interference ratios are almost independent of the cluster size and of the base station activities. The results demonstrate the dominance of the strongest interference and show that this dominance is even more pronounced in those situations when the signal to interference ratio is low. The presented results provide a base for more realistic models for performance evaluation in cellular systems than the commonly used Gaussian interference model.

Advanced antenna systems for WCDMA: link and system level results

This contribution presents some link and system level simulation results obtained by a WCDMA base station equipped with an adaptive antenna system. The results show that the performance gain obtained by an advanced antenna system could be substantial compared to an ordinary sector covering system. The link simulations show that for a given SIR target in a single cell system, the capacity is increased considerably compared to a conventional single sector covering antenna system. It is also shown that the difference between the different adaptive antenna algorithms is marginal. The system level simulations have shown that the capacity performance is basically proportional to the number of orthogonal beams used in the base station. In cases where the conventional three sector reference system is not truly interference limited, the performance gain can be even higher. The system simulations have also shown that using more beam positions than those defining the set of orthogonal fixed beams slightly improves the performance. However the number of beam positions can be kept relatively small, in the order of twice the number of orthogonal beams, without significant loss.

Capacity study for fixed multi beam antenna systems in a mixed service WCDMA system

Antenna arrays at the base stations allow capacity enhancement in cellular WCDMA networks. In this contribution we compare the relative downlink capacity between a system employing standard three sector site configurations with a system employing four fixed beam antenna systems. Since different packet services are expected to contribute largely to the traffic demand within a few years after initial deployment, this comparison is made in a mixed traffic environment. By realistic computer simulations it is found that a substantial gain can be expected by the introduction of adaptive (smart) antenna base stations. In this contribution a fixed multi beam system is considered, which is a fairly low complex adaptive antenna implementation. The simulations show that generally, a threefold capacity increase can be gained by employing a 4 beam antenna system. For some scenarios even higher gains can be achieved.

Antenna Configurations for 4x4 MIMO in LTE - Field Measurements

The 3GPP LTE standard for mobile broadband includes multi-antenna transmission modes that improve performance, both in terms of coverage, spectral efficiency and peak throughput. The antenna system design, both at the eNB and at the UE is critical to a well performing system; it should be designed with the intended performance profile in mind. Field trials were performed in order to investigate the relative performance of several four and two transmit antenna setups in an LTE system. In general, multi-antenna technology gave substantial performance gains over single antenna transmission. A closely spaced co-polarized configuration gave the best performance for users with poor channel quality while dual-polarized and well-spaced antenna configurations gave better performance for users with good channel quality. The trial also shows that UE antenna polarization is an important parameter that must be kept in mind when designing the eNB antenna system.

WCDMA 6-sector Deployment - Case Study of a Real Installed UMTS-FDD Network

Higher order sectorization is a promising technology to increase the capacity of cellular networks without the need for building additional sites. It is important to evaluate system performance in realistic non-homogenous deployment and traffic scenarios. A case study of a real network deployment has been undertaken to determine the capacity and coverage performance of the network when a limited set of sites are upgraded to 6-sectors sites. This in comparison to a homogenous and regular hexagonal scenario where a full network migration is performed. It is shown that the performance gain shown in homogenous deployments is maintained in a real network

Downlink capacity and coverage trade-offs in WCDMA with advanced antenna systems

Advanced antenna technologies are identified as one of the key techniques to improve the capacity and coverage of third generation WCDMA (FDD) systems. Advanced antennas can solve the capacity limitations in certain urban cells. Furthermore, they can also extend the coverage of large rural cells. The goal of this contribution is to highlight the downlink capacity and coverage gains and show the potential in capacity and coverage trade-offs for a WCDMA downlink provided by the use of advanced antenna systems installed at WCDMA base stations.

Adaptive antennas in WCDMA systems-link level simulation results based on typical user scenarios

This contribution presents some simulation results obtained by a WCDMA base station equipped with an adaptive antenna system. The results show that the performance gain obtained by an advanced antenna system could be substantial compared to an ordinary sector covering system. Migrating some existing sites/sectors to adaptive antenna systems can be seen as one attractive solution that increases capacity in a coverage area without condensing the system by building additional cell sites. To find out where this grow-on-site migration strategy is most beneficiary, it is important to evaluate the systems by taking typical user scenarios into account. The user scenarios includes spatially distribution of users as well as the expected user behavior related to the actual application (or user data rate). It has been shown that the gains using adaptive antennas for the investigated scenarios of non-uniformly distributed mixed service users are substantial.

LTE Downlink Inter-Cell Interference Assessment in an Existing GSM Metropolitan Deployment

In a loaded 1-reuse cellular network as e.g. 3GPP Long Term Evolution (LTE) the inter-cell interference limits the user bitrate for link adaptive packet data access. The cell isolation together with the link performance defines the spectrum efficiency and the achievable gain of higher order modulation or other link improving features. In this paper the cell isolation is measured as geometry factor in a dense city network. The measurements are performed on commercial GSM live traffic capturing the real spatial distribution including indoor usage. The cell plan of the studied metropolitan network is found to be very good and well optimised with the potential to support high user bitrates and high capacity for future LTE high speed radio accesses. The measured geometry factor distribution is superior to those that have been used for capacity evaluations in 3GPP indicating good performance of a possible LTE in existing deployments. A very good match between the live traffic measurements and simulations is found when introducing a tilted 3D antenna model into the cellular radio network simulation environment. Further, the tilted 3D antenna model results in a more realistic amount of interfering cells experienced at simulation estimations of spectrum efficiency.

MIMO Performance at 700MHz: Field Trials of LTE with Handheld UE

MIMO is one of the techniques used in LTE Release 8 to achieve very high data rates. A field trial was performed in a pre-commercial LTE network. The objective is to investigate how well MIMO works with realistically designed handhelds in band 13 (746-756 MHz in downlink). In total, three different handheld designs were tested using antenna mockups. In addition to the mockups, a reference antenna design with less stringent restrictions on physical size and excellent properties for MIMO was used. The trial comprised test drives in areas with different characteristics and with different network load levels. The effects of hands holding the devices and the effect of using the device inside a test vehicle were also investigated. In general, it is very clear from the trial that MIMO works very well and gives a substantial performance improvement at the tested carrier frequency if the antenna design of the hand-held is well made with respect to MIMO. In fact, the best of the handhelds performed similar to the reference antenna.